Being honest, let's talk about college football programs that really move the needle at a high level

You've got
SEC: Alabama, Georgia, Florida, Texas, Oklahoma for sure, maybe also Texas A&M, LSU, Tennessee
Big 10: Ohio St, Michigan, Penn St, maybe Wisconsin or Nebraska
ACC: Clemson, Florida St, maybe Miami
PAC12: USC, Oregon, maybe Washington
Big 12: None (though that does leave a power vacuum that could benefit BYU)
Other: Notre Dame

So right now, there's anywhere between 5-7 programs outside the Big 10/SEC that really have a national reputation at the highest level.

If the Big 10 takes 3 of those few remaining programs, it solidifies things a lot more as just a power struggle between those two conferences.

In that case, it's very much within the realm of possibility that the Big 10 adds USC, Stanford, Washington, Oregon to go to 18 teams.

The SEC responds by adding Clemson, Florida St, Miami...and maybe North Carolina? As the lone power team outside the Big10/SEC, Notre Dame then goes to the Big 10.

And as the dust settles, you go from P5/G5/FCS to a situation where there's effectively two superconferences who compete amongst themselves basically the way the Europen superleague was designed to for soccer. And the remaining 3 P5 conferences become officially second tier.